Urinary incontinence, in other words, the involuntary leakage of urine, affects up to twenty percent of the population across all ages. Incontinence can be divided into categories. Urge incontinence describes a condition where a person has a sudden need to pass water is unable to prevent bladder contraction and, thus, urine leakage, until they can reach a toilet. This condition can be associated with an unstable or overactive bladder. Stress incontinence is a condition where urine is leaked in response to sudden pressure on the bladder that the sphincter cannot withstand. For instance, urine leakage may occur in response when laughing, coughing or from sudden movements such as jumping. This condition is often associated with an incompetent striated urethral sphincter. Also, a person may suffer from a combination of urge incontinence and stress incontinence, known as mixed incontinence.
Incontinence can arise from a number of possible causes, including conditions associated with child birth injuries, that weaken the urethral sphincter and/or pelvic floor muscles, prostate surgery, disease and idiopathic problems. In patients who have suffered a spinal trauma, the nerves and reflexes controlling the bladder may be affected, leading to incontinence.
Normally, the sphincter is controlled from the central nervous system, via the pudendal nerves. These nerves, which originate in the sacral spinal cord, course through the sacral nerve roots and then on to the pelvic floor and sphincter. En route, the pudendal nerves pass close to the rectum and comprise a motor and sensory division. Activity in the pudendal sensory nerves, together with descending signals from the brain, help to prevent the bladder contracting involuntarily while it is filling, by means of inhibitory pathways in the spinal cord. The bladder and sphincters are normally coordinated by the brain stem and, when the bladder is full, it is these pathways, together with social and cognitive factors, that determine when the conditions are right for micturition.
In addition, other mechanisms normally act to prevent involuntary leakage of urine. During coughing, straining or other actions causing pressure in the abdomen, both the urethral and anal sphincters contract reflexly to prevent incontinence. Furthermore, the tone of the urethral and anal sphincters increase automatically as the bladder fills, to prevent leakage. This is known as the “guarding reflex”.
For some years, methods involving electrical stimulation of the sacral nerves have been used to help prevent incontinence. The stimulation of one neural pathway to control the activity in another neural pathway is commonly known as neuromodulation. The stimulation may be excitatory or inhibitory. A review of some of these techniques is given by Craggs M. D. in “Textbook of the Neurogenic Bladder, Adults & Children”, Corcos J. & Schick E. (eds.), 2004, London: Martin Dunitz, pp 625-635. At low levels of stimulation, an overactive bladder can be controlled via spinal cord inhibitory pathways. At higher levels of stimulation, the sphincter muscle is also brought into direct action via its pudendal motor nerves. These techniques can be combined to provide a therapy for controlling urinary incontinence.
Previously, neuromodulation has been effected with devices comprising stimulating electrodes for placement at various positions, for example, in the anal canal, vagina or skin sites in the region of the pudenda, such as the dorsal penis, dorsal clitoris or perineum. In all these positions, it is possible to activate sacral reflexes by continuously stimulating different branches of the sensory pudendal nerves, which are able to suppress or inhibit an overactive bladder.
More recently, implanted devices have been developed that can reproduce these benefits by applying continuous stimulation through electrodes placed at various sites along the route of the pudendal nerves to the sacral spinal cord. The most common site for such implanted electrodes has been the point at which the sacral nerve roots leave the spinal cord through the sacral foramina.
Such devices suffer from the drawback that the stimulation provided may become ineffective through habituation, following continuous stimulation of the spinal pathways. This problem has been addressed by providing conditional stimulation devices. US 2005/0113881 A1 discloses a prior implanted device arranged to provide stimulation in response to certain conditions. The device includes a sensor that detects motion of or pressure in the bladder via signals conveyed by the muscles of a patient. If the output of the sensor suggests that there is a likelihood of involuntary urine flow, the device stimulates the muscles to inhibit urine flow. Another prior implanted device is disclosed in U.S. Pat. No. 6,836,684, and is arranged to provide conditional stimulation to the nerves of a patient based on events detected via nerve signals.
For many patients, an implant is often inappropriate. The implantation of a stimulator device is a surgical procedure and is thus associated with a degree of risk. Furthermore, an implanted device cannot be serviced or removed easily as this would require further surgical intervention. Such devices are sometimes also unsuitable for treatment of children, due to their rapid growth. However, there are also drawbacks associated with non-implanted devices, as they may be uncomfortable, unsuitable for prolonged treatment sessions or difficult to insert and remove.
Thus, both implanted and non-implanted devices have drawbacks that increase the probability that a patient will abandon their therapy in favour of other methods of treatment. However, the available alternative treatments, such as drugs and incontinence pads have their own disadvantages, such as side-effects, lack of comfort or convenience and social stigma.